Just thought I'd share this method I've recently started using when shooting from hides.

I recently bought a gimbal head to make shooting with my Sigma 150-600m a lot more manageable (one of the best accessories I've ever bought I think). Having recently decided to have a go at bird photography I started frequenting hides at reserves like Abberton reservoir (near Colchester) but found setting up my tripod awkward because the bench seats in the hide got in the way. I could shoot from the corner openings but that meant standing up which I struggle to do sometimes (due to a medical condition).

Every now and then in life you ponder a problem and come up with a possible solution, only to find it already exists

In my case it's the Manfrotto 349 column clamp. This allows me to clamp my tripod's centre column, complete with gimbal head, to the drop-down flaps in the hide. The flaps are normally heavy duty and well-supported so no issues with weight once the camera and lens are fitted.

The result is a comfortable shooting position The whole assembly can be adjusted up or down to get the camera's eyepiece in the right position.

The picture below I took on my phone so the quality is not brilliant but it shows the clamp in-situ (plus a wind-swept 'er indoors on target spotting duty!)

I got mine from Amazon but I'm in no way affiliated to them! I believe there are two sizes of clamp so you have to make sure your centre column will fit. Fairly straightforward for me as my tripod is a Manfrotto anyway. It has a rounded triangular shaped centre column but the clamp works fine with it.

I think that the best solution depends on the design of the hide. Your solution seems good for the window hatch design in your hide. Most that I see have upward opening hatches with a single shelf running along below the window.

I use a small ballhead on the monopod, I have tried a pistol grip, easier to use but clumsy to carry as I expect the monopod to double as a walking pole.